Swivels have long been provided in fluid lines to allow rotation of one line component with respect to another line component. While some prior art swivels allow only limited angular rotation of these components, many swivels allow rotation about 360 degrees, and allow numerous repeated rotations. In many applications, a conventional O-ring seal within the swivel maintains a desired fluid tight seal between the upstream and downstream swivel components in a cost effective and reliable manner. In other applications, reliable sealing between swivel components cannot be maintained over an extended period of time. In some instances, the fluid being transmitted through the swivel deteriorates the swivel seal, while in other applications the swivel is subjected to jarring, bumping, or shock from any number of sources which damage the seal or sealing surface, and/or otherwise cause pressurized fluid to leak past the seal.
One application which has long presented a problem with obtaining a reliable and cost effective seal concerns the transportation of certain petroleum products or other fluids, such as anhydrous ammonia, which are deleterious to conventional elastomeric seals. In many instances, a flexible hose is used to interconnect a supply tank with a storage tank or other vessel to be filled, and a discharge valve is accordingly provided at the free end of the hose. Those familiar with hoses recognize that hose twisting is inevitably required to position the discharge nozzle at the inlet of the tank or other vessel prior to filling, and a swivel is thus preferably used upstream of the discharge valve to reduce "fighting" the hose to this desired position. Some hoses are manufactured from materials and/or with wall thicknesses that result in a stiff hose, thereby requiring more effort or fighting to desirably position the end of the hose. Hose fighting is also increased when fluid pressure in the hose increases. Rotation of a component at the end of a hose occurs as the hose is reeled about or unwound from a hose reel, and this rotation substantially increases the hose fighting required to position the discharge end of a hose at a fill site. When the hose is rewound onto the reel, this rotation causes the fill valve or other component at the end of the hose to rotate, which increases the likelihood of shock or damage to the component.
Even though liquid hydrocarbons are passed through a swivel, in some applications, such as hydraulic applications or gasoline filling operations, this swivel may use conventional O-ring technology to maintain a reliable seal due to the characteristics of the fluid and the relatively low fluid pressure passing through the swivel. Those familiar with gasoline service stations from decades past may remember the difficulty associated with filling a car with gas utilizing a hose which does not contain a swivel, and the relative ease of performing the same operation with today's gas pump hose having a swivel both at the stationery pump/hose connection, and most importantly at the hose/gas discharge valve connection.
The type of swivel successfully used at gasoline service stations unfortunately cannot be reliably used in other applications. When filling a liquified petroleum gas (LPG) or propane tank at a house or business, the operator of the delivery truck or bobtail typically utilizes a hose 20 meters long or more to connect the portable fill tank with the stationery tank to be refilled. While a gasoline-type swivel has been tried between the free end of the hose and the fill valve, such a swivel has a very short life since the seal soon starts to leak, primarily due to the fluid "drying out" the O-ring seal. Due to the high unreliability of these conventional swivels, many companies and/or operators use no swivels on their equipment to justifiably minimize safety and environmental concerns. While many individuals have some experience with "fighting" a gasoline fill hose, few people other than bobtail operators appreciate the extreme effort associated with fighting a 30 meter long LPG hose during freezing outdoor temperatures in order to properly position the fill valve at the inlet of a homeowner's heating tank.
A product referred to as the Full Circle swivel was recently introduced to the market to provide a more reliable connection between a liquified gas hose and a fill valve. This swivel relies on a mechanical seal of the type commonly employed in pumps to seal between the upstream and downstream swivel components. Two dynamic sealing faces must thus be maintained, with the mechanical seal rotating at one half the speed of one swivel component relative to the other swivel component. While this swivel does alleviate hose fighting and simplifies the fill valve to fill tank connection, the swivel has a number of other disadvantages. The swivel is costly since the mechanical seal must reliably seal with two different high-tolerance sealing faces. Due to the nature of this swivel connection, extreme care must be taken to avoid jarring or shock to the swivel, although those familiar with bobtail filling operations recognize that the free end of the filling hose often is dragged along the ground when the hose is rewound after the filling operation. The torque required to cause rotation between the swivel components of this product also varies as a function of the fluid pressure through the swivel, since increased sealing force is generated by increased fluid pressure. Since LPG filling pressure may vary from less than 100 PSI to over 300 PSI, the swivel may serve its desired purpose under low fluid pressure conditions, but substantially increased torque is required to cause rotation of the swivel under higher fluid pressure conditions. In addition to being expensive to manufacture and maintain, leakage of the Full Circle swivel cannot be checked with conventional soap bubble-type leak detector liquids since these solutions damage the mechanical seal of the swivel.
These and further disadvantages of the prior art are overcome by the present invention, and an improved swivel is discussed in detail below. The swivel of the present invention has particular utility with respect to connections to hoses used for transmitting fluids which are otherwise deleterious to conventional O-ring seals, such a propane, LPG, or anhydrous ammonia.